Abstract
One of the largest (36km2) Late Holocene systems anywhere in Ontario lies in Pinery Provincial Park on the southeast coast of Lake Huron and postdates a 12‐km‐long beach barrier system left by Lake Nipissing some 5000years ago. Dunes lie parallel to the lake shoreline, oblique to the dominant west–northwest wind. Linear dunes in the north of the field regardless of age are stable and of moderate height (<10m) having grown in situ from foredunes on emergent beach ridges. Southwards however, the same dunes evolve into wider, higher (up to 20m) parabolic forms with large blow outs. This change in form from north to south appears to have been a persistent evolutionary trend over the past 5000years. Some 5km of high resolution radar profiles identifies the changing internal stratigraphy of dunes as they evolve in shape. Linear dunes are composed of a ‘vertical aggradation sequence’ (VAS) that records initial formation of a foredune on top of shore-parallel beach ridges, and upwards growth of the dune by sand trapped by vegetation. Southwards over some 12km, dunes grow in height and assume a parabolic form expressed on radar profiles by a lowermost VAS overlain by cross-bedded sand comprising a landward accretion sequence (LAS) recording landward migration. A depositional model relates the change in dune shape and stratigraphy to southward increasing sand supply within a large persistent littoral cell in Lake Huron.
Published Version
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